Fibrinolytic agents used in intravenous thrombolytic therapy of myocardial infarction also exert, at effective dosages, significant side effects on the haemostatic system outside the direct resolution of the target thrombus. The side effects of the agents streptokinase and anisyolated plasminogen-streptokinase activator complex are larger than the side effects of the more fibrin-specific agents tissue-type plasminogen activator and pro-urokinase. An important difference between the two groups of compounds is that the major plasmin inhibitor alpha 2-antiplasmin is completely exhausted for the first two agents, but only in part of the cases for the fibrin-specific agents. The effects on various factors in the fibrinolytic cascade on the plasminogen activator, plasminogen-plasmin and fibrinogen-fibrin levels are reviewed concisely.